STRAPAROLLUS. 317 
249. Disconetix spinosus, Wright, MS. Plate XXV, fig. 8. 
1859. STRAPAROLLUS SPINOSUS (name only), Wright. Quart. Journ. Geol. Soc., 
vol. xvi, p. 36. 
1873. ? — sp., Tawney. Dundry Gasteropoda, p. 36 (28). 
Cf. also — suBmQuALIS, d’Orbigny. Terr. Jur., vol. ii, p. 311, pl. 322, 
figs. 8—11. 
Description : 
Diameter (fair size). : : . 24 mm. 
Height 3 ‘ : ‘ . 8mm. 
Diameter of largest specimen known : . 46 mm. 
Shell depressed, discoidal, upper and under surfaces nearly equally excavated. 
The whorls are subquadrangular, with sides almost perfectly flat, and the 
marginal keels are largely tuberculated at intervals. The spiral ornamentation is 
so fine as in many cases not to be detected; this is decussated with somewhat 
rugose strize of growth, perpendicular or curved. In the larger shells the 
marginal tuberculation extends in ill-defined swellings or cost right across the 
body-whorl. Aperture quadrangular, spiral and axial diameters nearly equal. 
Relations and Distribution.—This species is by far the largest of any described 
under Discohelix-Straparollus from the Inferior Oolite of this country.’ It most 
resembles Straparollus subequalis, a’ Orbigny, from the Inferior Oolite of Fontenay 
and Niort, both as to habit of growth and general character, but the marginal 
tuberculations present a considerable difference. It is also related to Straparollus 
tuberculosus, Thorent, but is truly biconcave and dextral. From all other British 
species of Discohelix and Sjraparollus, except the one next described, it may be 
separated by the fineness of the spiral ornamentation. In many specimens this 
is so fine that the shells appear smooth, though this appearance, no doubt, is 
partly due to wear. 
Discoheliz spinosus occurs principally in the concavus-bed of Bradford Abbas, 
where it is rather rare. 
250. SrRAPAROLLUS ‘‘ TUBERCULOSUS-DEXTER.” Plate XXVI, fig. 1. 
1854. Evompsatus ruBercuLosus, Thorent, sp. Morris, Cat., p. 248. 
Cf. — — — Mém. Soe. Géol. France (1839), vol. 
ili, pt. 2, p. 259, pl. xxii, fig. 8. 
Bibliography, §c.—To a certain extent the specific name “ tuberculosus” is 
applicable to all species of Discohelix and Straparollus described in this Mono- 
1 Owing to unequal enlargement, and to the selection of medium-sized specimens, this fact is not 
made sufficiently evident in the plates. 
